With the advent of low-cost microprocessors, pen plotters with high speed and resolution have become increasingly sophisticated. Such pen plotters, which are usually driven by command from an external computer, include a means for supporting paper or other medium, a mechanism for moving the paper back and forth during plotting, a carriage which supports a pen during the plotting operation, a mechanism for moving the carriage normal to the movement of the paper during plotting, a pen turret for storing a plurality of pens for use in plotting, and a mechanism for rotating the turret.
The use of a pen turret permits utilization of a plurality of pens, such as different colors, different pen tip widths, and the like to provide a variety of pen plots. Conventionally, the pen turret is rotated by a separate motor, mechanically coupled to the turret. The microprocessor permits the operator to select the sequence of pens to be used in the plot and then drives the pen turret motor at the appropriate time to rotate the turret when a particular pen is to be selected therefrom.
In one variety of plotter, the turret motor is coupled to the pen turret by geneva motion. However, while this system is reliable and accurate, it does require a separate motor to drive the pen turret.
In another variety of plotter, the pen turret has a ring gear turned by a very accurate stepper motor, with light sources and detectors to sense the pen positions. However, this system not only requires a separate motor to drive the pen turret, but it also is very expensive and is more complex than the geneva motion.
Such plotters work fine, but attempts continue to find ways to improve performance, cut cost, reduce weight and the like.